Organochlorine insecticide use and risk of non-Hodgkin lymphoma: findings from the North American Pooled Project

Abstract

INTRODUCTION: Organochlorine insecticides are persistent, bio-accumulative compounds that are frequently used worldwide. Recently, the International Agency for Research on Cancer (IARC) classified several organochlorines as Group 1 and 2A carcinogens for non-Hodgkin lymphoma (NHL). However, some previous studies had limited statistical power and did not assess exposure-response relationships. We investigated self-reported organochlorine exposure and NHL risk in a large population-based study: the North American Pooled Project (NAPP). METHODS: Four case-control studies conducted in Canada (1991-1994) and Midwestern U.S. (1981-1986) were pooled to form the NAPP, which includes 1690 NHL cases and 5131 controls. Odds ratios (OR) and 95% confidence intervals (CI) for ever/never use and duration of use (years), were estimated using logistic regression with adjustment for demographic characteristics and NHL risk factors. RESULTS: Compared to unexposed subjects, statistically significant associations with NHL risk were observed among those reporting use of chlordane (OR=1.44, 95% CI=1.13-1.84), DDT (OR=1.32, 1.10-1.58), dieldrin (OR=1.52, 1.04-2.22), heptachlor (OR=1.47, 1.02-2.11) and lindane (OR=1.69, 1.31-2.17). A consistent exposure-response trend was observed for years of lindane use: OR >0-5=1.36, OR 5->10=1.87, OR 10->15=1.93, OR >15=2.01 (p-trend=<.0001). Increased risk of NHL was observed for >15 years of DDT use (OR=1.52, 1.06-2.17, p-trend=0.001). Non-monotonic positive trends in risk were also observed for years of chlordane (p-trend=0.03) and heptachlor (p-trend=0.04) use. Conclusions: This analysis uncovered statistically significant associations for several organochlorines and NHL risk. The sample size of the NAPP allowed us to estimate risk across more refined exposure levels and identify significant exposure-response trends for lindane. Overall, these findings contribute to the epidemiologic literature supporting the recent IARC classifications.